A thermal printer prints images by transferring donor material from a donor ribbon onto a receiver medium. Typically this is done by selectively heating the donor ribbon to melt donor material while concurrently pressuring the donor ribbon against the receiver medium. In this way, melted donor material transfers from the donor ribbon to the receiver medium to form an image while unmelted donor material remains on the donor ribbon. Donor ribbon is typically connected between a supply spool, which initially carries a supply unused donor ribbon, and a take-up spool upon which used donor ribbon is wound. In operation, the take-up spool is rotated to draw donor ribbon from the supply spool and across the print head for use in printing.
The donor spool and take-up spool can be provided as independent rolls joined only by the donor web. Alternatively, the donor spool and take-up spool can be joined together by a structural framework to form a thermal donor cartridge. Such a thermal donor cartridge provides a rigid structure around the supply spool and the take-up spool that can be used to protect the donor ribbon from incidental contact and from contaminants and that also positions the supply spool and the take-up spool in a geometric relationship. A wide variety of thermal printer cartridge designs are known. Typically each thermal printer cartridge is designed to be used in one particular type of thermal printer.
As thermal printing has grown in popularity, particularly in consumer applications, there has been a demand for thermal printer cartridges that can hold larger amounts of donor ribbon. However, the design of such high quantity thermal printer cartridges creates unique design problems. One of the most difficult problems is the challenge of creating a low cost and high quality cartridge which can survive the sometimes torturous environment that a typical consumer will subject it to. This is because the relatively large supply of thermal donor ribbon in such a thermal donor cartridge increases the weight of the thermal donor cartridge, which in turn, substantially increases the kinetic energy that the cartridge must be able to dissipate during a fall or drop or other impact incident.
In particular, it will be appreciated that when the donor cartridge is subjected to an impact load, a substantial shock wave permeates the donor cartridge. The energy from such a shock wave must be managed by the structures of the thermal printer cartridge in a way that allows the energy from an impact to be dissipated without non-elastic deformation of the thermal printer cartridge that could interfere with the use of a dropped thermal cartridge.
Accordingly, the design of a high load thermal printer cartridge is typically adapted to address this issue. One way in which this can be addressed is to provide a more rigid thermal donor cartridge which can be done by using materials such as metals or expensive, high modulus of elasticity materials to form the thermal donor cartridge or to form the thermal donor cartridge using large, heavy, stiff structural forms. Alternatively, energy absorbing features can be incorporated into the exterior of the donor cartridge such as by applying cushioning bumpers to the thermal donor cartridge. These methods however, increase the size, weight and cost of the thermal printer cartridge.
What is needed is a low cost thermal printer cartridge that is adapted to manage relatively high kinetic energy loads.